There has been little systematic work on diet selection in experimental diabetes. We have found that some rats, notably those that seem to have the most severe diabetes, reject high fat diets, a finding which contradicts a common belief that fat is good for these animals. We propose to examine the food intake and food selection of rats prepared with varing degrees of diabetes after streptozotocin injection or partial pancreatectomy. We shall examine the influence of fat content and of protein to calorie ratio upon diet selection in these animals. We shall determine the functional severity of diabetes in the same rats by measuring their insulinogenic reserve, by a glucose tolerance test and other metabolic measurements. We propose to measure the feeding patterns of diabetic rats on the various diets, and to simultaneously measure the EEG; we shall then correlate meal size with intermeal interval lengths and sleep events. These data will provide a good understanding of the relationship between metabolic state and behavior in these animals. We shall investigate the possible role of the brain neurotransmitter, serotonin, as a mediator of both satiety and sleep events. By measuring brain serotonin levels, and the concentrations of its precursors and metabolites in diabetics fed the various diets, it will be possible to assess the role of this system in the behavior described. The results will provide comprehensive data on the relationship between diet composition, hormonal status, and neurochemistry.